To help identify specific factors in the etiology of schizophrenia, the proposed research uses recently developed strategies for dealing with probable etiologic heterogeneity in schizophrenia. These strategies involve the intensive study of families with single vs multiple cases of schizophrenia. Schizophrenics in such "simplex" and "multiplex" families will be given a research diagnostic interview schedule, as well as several measures, including visual tracking, though disorder, attention, platelet MAO, and perinatal complications. Nonschizophrenic members of multiplex families and a group or normal subjects will also be studied. The study's broad objectives include the elucidation of variables that distinguish etiologic subtypes of schizophrenia, and can serve as indicators of specific genetic and environmental factors in their respective etiologies. Of particular interest would be the identification of factors that a) distinguish schizophrenics in simplex vs. multiplex families, b) have a distribution in several large families consistent with Mendelian transmission in a schizophrenic subtype, or c) that distinguish schizophrenics and their unaffected relatives who carry the same putative marker for genetic vulnerability, thereby suggesting an etiologic role for particular environmental factors. Identification of etiologic factors for different subtypes of schizophrenia could have considerable clinical as well as research significance, since different subtypes could involve different courses, treatment responses, and prevention strategies. This application requests funding that is critically needed for a pilot study that involves an innovative research strategy and is directed by a relatively junior principal investigator. As such, the proposed research seems well-matched to the aims of the NIMH Small Grant Program.